My Heater/ac 1 & 2 Does Not Work

When I Try To Put On My Heater Or A/c, Levels 1 & 2 Does Not Work But 3-5 Does. But When I Do Use The Heater And Put It On 3, The Heater Works For About A Min Or So, Then It Begins To Blow Out Cool Air Instead Of Hot Air.does Anyone Know What The Problem Is Or How Can I Fix This Problem, Cause I Live In Jersey N Its Freaking Cooooooold!..lol...

Buy The Way , This Is For My 2000 Chevy Malibu Ls

You have 2 problems, one the blower motor resistor is burned out, and your heater core is plugged.

what do u mean by my heater core is plugged?